This invention relates to bark articles, and has particular reference to a method of extruding articles, such as solid synthetic fuels and fireplace logs comprising mostly bark.
Heretofore, extrusion techniques have not been successful as methods of forming bark articles. Bark has heretofore been extremely difficult to extrude for several reasons. It has a high moisture content, usually about 50% and must be dried to prevent extruder heat, and compressional and frictional heat from changing the moisture to steam and causing explosions within the extruder. Also, dried bark does not readily flow through an extruder. Dried bark is hard and does not sufficiently adhere to the interior surface of extruder barrel wall to allow the extruder screw to pass the bark on through the extruder. Rather, bark tends to turn with and remain with the screw in the extruder. Further, bark often chars or burns due to heat during the extrusion process. Still further, bark is not easily extrudable through a die into the form of a solid article since natural resins in bark are not adequate to bind pieces of bark together at an economical rate of speed.
It would therefore be desirable to provide a method of extruding bark into the form of formed articles comprising mostly bark, which overcomes the aforementioned extrusion and forming problems.
Methods of extruding bark according to this invention virtually eliminate the likelihood of explosions since they involve drying the bark to less than 7% moisture. Also, a thermoplastic binder is added to the bark so that the bark-thermoplastic mixture sufficiently adheres to the interior surface of the extruder barrel wall to allow the screw to pass the bark through the extruder. Further, temperature of the bark and the extruder are controlled so that the bark does not char or burn during the extrusion process. The thermoplastic binder for bark cooperates with natural resins therein and adequately binds the bark pieces together so that solid articles such as synthetic fuels which can be in the form of fireplace logs can readily be formed.
Although synthetic fuels are known and have been made in various forms including those for home use such as briquettes and fireplace logs, such articles, when made by conventional methods, have had most any combination of shortcomings. For example, such synthetic fireplace logs often are loosely packed, improperly bonded, flaky and dirty to the touch. They often are unnatural-looking since many have decorated paper wrappings and they can be too heavy for certain consumers. The logs also often are very sensitive to moisture, difficult to light, unpleasant odor-producing, and of low fuel value. Further, the materials used to make conventional synthetic fuels often have other useful purposes. For example, sawdust and wood chips often can be used for making paperboard or other wood-derived products such as particleboards.
It would therefore be desirable to provide a method of making articles such as synthetic fuels which overcome the aforementioned shortcomings.
The solid article, synthetic fuel or fireplace log made according to the method of this invention is well-bonded and solid, does not flake or come apart, has a smooth, hard finish and is clean to the touch. It has a natural wood-like appearance without the use of decorated wrappings, it weighs less than some presently commercial synthetic logs, and is only slightly moisture sensitive. The logs light easily, burn quietly and cleanly and have a higher fuel value than wood itself.
The bark, combustible thermoplastic and waxed paper waste materials used to make the solid synthetic fuel, or fireplace log of this invention often have no other apparent useful purpose, and are often considered of negative value. Most of the multi-million tons of such waste materials produced each year must be deposited at and/or burned at dump areas. The method of making the solid article, synthetic fuel or fireplace log of this invention is therefore economically and ecologically advantageous because it provides an important, valuable fuel use for the aforementioned waste materials.
Numerous other objects and advantages of the invention will be apparent as it is better understood from the following description, which, taken in connection with the accompanying drawing, discloses a preferred embodiment thereof.